Osteological comparisons of appendicular skeletons: a case study on Patagonian huemul deer and its implications for conservation

Abstract

Early explorers described huemul (Hippocamelus bisulcus) as stocky, massive and short-legged deer ofmountains, comparing them to ibex (Cabra ibex), chamois (Rupicapra rupicapra), mountain sheep (Ovis canadensis)and mountain goats (Oreamnos americanus). Subsequent key paleontological work also claimed that huemul are mountaindeer. However, all these comparisons of huemul to other ungulates were done without any supporting data. These historicevents lead to: (i) the continued prevailing claim that huemul are mountain deer; and (ii) that their natural range is the Andeanmountains, as evidenced by the current distribution. We found that early writings about huemul generally reported theirrareness, disappearance or near extinction. References to stocky and short-legged huemul were casual remarks made aboutdeer found mainly in refuge areas. Paleontological comparisons were based on a new fossil labelled as mountain deerwhich, however, has been shown to be a construct and declared a ‘nomen nudum’. Behaviour like the aggressive horseshoestance and thick long hair dissimulate stockiness by distorting body shape. Comparing leg morphometrics of huemul and12 other ungulates revealed that huemul cannot be associated with rock climbing species. Intraspecific proportional leglength is not static and is influenced by ecogeography, nutrition, physiology and factors affecting exercise. Thus, climate,altitudinal hypoxia and locomotor pattern employed according to terrain, predation and forage affect the appendicularskeleton. Nutritional deficiencies occurring in Andean mountains are notorious for affecting bone development, causingosteopathology and altering body shape. Frequent underdeveloped huemul antlers and high incidence of osteopathologysupport the effect from mineral deficiencies. Skeletal proportions are affected by numerous factors, causing largeintraspecific variation. Relative metapodial length varies up to 70% in better studied cervids, and populations fromdifferent environments can be clearly distinguished. Huemul morphology does not overlap with rock climbing speciespreviously considered analogous, but falls within the range of other cervids. We caution against the rigid application ofmodern huemul occurrences in interpreting past habitat use. The few historic extra-Andean accounts cannot be consideredabnormal outliers. Huemul ecology must be interpreted in terms of first principles rather than applying direct analoguesfrom the present. This allows us to begin to use the past to understand the present instead of repeating the fallacy of imposingthe present on the past. Current efforts to recover remaining huemul are distinctly based on the assumption that huemulforemost belong in rugged mountains, because of their supposed special adaptions and resemblance to stereotype ungulates,also erroneously believed to only occur in rugged mountains elsewhere.Weconclude that the present empirical comparisonssupport many other lines of evidence that huemul existed in treeless habitat and colonised Andean forests and higheraltitudes secondarily. Habitat breath of huemul is thus more like that found in other closely related Odocoilines, promisingtremendous new opportunities for recovery efforts.